Can I call a derived class's function in base class?

Question

I have a function d() in a derived class, which is to be called in a base class function b(). I tried to do this by making a virtual function with the same name in the base class(to satisfy the compiler and to enforce late binding). I will always be calling the b() using an object of derived class. But the problem is that compilation goes fine, but linker is returning an error:

undefined symbol <baseclass_name>::d in module main.cpp   

the Weird thing is that d() is not even called in main.cpp. It is defined and called in another file.

I am stuck here. Can anyone give any possible explanations or suggest a better method?

(I need to call d() from base class or it will make my code even more bulky...)

Answer 1

You'll need to either implement the base-class version, or declare it pure virtual in the base class (or both), depending on whether it makes sense for the base class to implement it. All non-pure virtual function must be implemented, which is probably why you get that error.

Answer 2

Template method pattern may help you, declare the function pure virtual on base class and implement it on the derived class. And use the function normally on base class.

Answer 3

I think your problem might not be C++ but linkage. If you put your d() in another cpp file you will have to compile and link those files together. For example:

g++ main.cpp a.cpp b.cpp -o test

This will compile the three .cpp files and link them together into the executable called 'test'.

If you are using an IDE you might have to create a project and add all required cpp files to it. When you build all the files in the project will be used to build your executable.